Jumping Between Characters and Their Missions

Hi

As per the above I have noticed that when I jump between characters, when not on a mission, it tells me how many missions that character has avaliable. My question is... if I jump between characters in a random order will I get to play all of that characters missions or is it dependent on who you pick first?

Is the first time you can move between characters just after Franklin helps Michael recover his yacht and rescue his son? Many thanks in advance for any advice/info given.